Bigtimer - the guys that shoot BH209 are probably better suited to answer your question. But from what I've seen on here I think BH209 works best with heavier charges (like 100+ grains).
I was just down Wal-mart and picked up two canisters of Pyrodex RS on sale. With that I know you could start with 80 grains and still have plenty of power to take down a deer.
BTW congrats on the deal. I hope your daughter likes it.